An earthquake registering 7.6 Mw, one of the deadliest in history, devastated Tangshan, China, and killed at least 240,000 people.

The 1976 Tangshan earthquake was a M_w 7.6 earthquake that hit the region around Tangshan, Hebei, China, at 19:42:55 UTC on 27 July. The maximum intensity of the earthquake was XI (Extreme) on the Mercalli scale. In minutes, 85 percent of the buildings in Tangshan collapsed or were rendered unusable, all services failed, and most of the highway and railway bridges collapsed or were seriously damaged. The official count stated 242,469 deaths, while historians accepted at least 300,000 died, making it the deadliest earthquake in recorded history and one of the worst disasters in China by death toll.

The moment magnitude scale is a measure of an earthquake's magnitude based on its seismic moment. M_w  was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Similar to the local magnitude/Richter scale (M_L ) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale.

Tangshan is a coastal, industrial prefecture-level city in the northeast of Hebei province. It is located in the eastern part of Hebei Province and the northeastern part of the North China Plain. It is located in the central area of the Bohai Rim and serves as the main traffic corridor to the Northeast. The city faces the Bohai Sea in the south, the Yan Mountains in the north, Qinhuangdao across the Luan River to the east, and Tianjin to the west.